Spatial and temporal variations of bacterioplankton in a subAntarctic coastal area (Kerguelen Archipelago)

Bacterial abundance and production were measured monthly for one year along cross-shore transects (seven stations each) carried out in 3 subAntarctic fjords of the Kerguelen Archipelago. Mean values of the 3 most coastal (inside) and most offshore (outside) stations were used to describe the relationship between temperature, phytoplankton biomass, bacterial abundance and bacterial production over an annual cycle. All the sampling protocol was repeated two times during each cruise: at noon and midnight. During the entire sampling period temperature ranged from 2.1 to 7.4 °C, chlorophyll a concentrations varied by a factor of 10, bacterial abundance by a factor of 12 and bacterial production by a factor of 30. Over one day, all these parameters could vary by a factor of 4 between noon and midnight. A clear seasonality was observed for all the parameters. However, while variations of phytoplankton and bacterial production paralleled those of temperature, bacterial abundance is low in midsummer and maximum in autumn. While no general pattern could be observed from the total data set, spatial gradients could interfere strongly with temporal changes.